The present invention generally relates to energy transfer indicators for chemical sensors used in monitoring, detecting and/or measuring parameters at locations remote from detection instrumentation. More particularly, the invention relates to chemical sensor components that incorporate tethered pair fluorescence energy transfer indicators which are suitable for being positioned at a remote or distal portion of an optical fiber waveguide. These chemical sensor components incorporate a spacer of a known or a determinable length that tethers together a colorimetric indicator or acceptor and a fluorescent energy donor, and the absorbance spectrum of the colorimetric indicator overlaps with the emission spectrum of the fluorescent donor.
Fiber optical chemical sensors are generally known to be useful for a wide variety of purposes, especially in the areas of medicine, scientific research, industrial applications, and the like. Descriptive materials that discuss the structure, properties, functions and operational details of fiber optic chemical sensors include Hirschfeld U.S. Pat. No. 4,577,109 and Sietz, "Chemical Sensors Based on Fiber Optics", Analytical Chemistry, Vol. 56, No. 1, January, 1984, each of which is incorporated by reference hereinto. From publications such as these, it is known to incorporate a chemical sensor into a fiber optic waveguide in a manner such that the chemical sensor will interact with an analyte. The chemical sensor composition and analyte interaction results in a change in optical properties, which change is probed and detected through the fiber optic waveguide. These optical properties of the chemical sensor compositions typically involve changes in colors or in color intensities. In these types of systems, it is possible to detect particularly minute changes in the parameter being monitored in order to thereby provide especially sensitive monitoring capabilities.
A specific application of this fiber optic chemical sensor technology is found in Peterson et al U.S. Pat. No. 4,200,110, which shows a fiber optic pH probe. This patent is incorporated by reference hereinto. Other parameters that are typically suitable for measurement by fiber optic chemical sensors include oxygen concentrations and carbon dioxide concentrations which, together with pH, are typical blood parameters that need to be monitored in vivo. Fiber optic chemical sensors can also be used to detect metal ions such as Al.sup.+++ and Be.sup.++ and other metal ions that can be determined fluorometrically when in solution, including Mg.sup.++, Zn.sup.++ and Cd.sup.++. Other uses for these types of devices include detection of biological fluids, glucose, ammonia, UO.sup.++ and halides, the detection of which may require that reagents be diffused into the sample. Other areas in which fiber optic chemical sensors may be useful include the monitoring of chemical conditions during industrial processes, such as for taking industrial biological measurements. An example of a specific industrial type of application could include the use of long-length optical fibers in order to measure conditions within submerged wells or the like.
A typical approach in the construction of fiber optic chemical sensors requires the positioning of a dye material or other chemical indicator at a generally distal location with the assistance of various different support means. The support means must be such as to permit interaction between the dye material and the substance being subjected to monitoring, measurement and/or detection. Exemplary means include permeable membranes, microencapsulation, and the use of a gel-like support. Chemical indicators for such chemical sensors and the like include sensors that are based on the absorbance of dye materials which are covalently bound to polymer materials. An example is found in the Sietz article "Chemical Sensors Based on Fiber Optics", supra.
Proposals have been made, for example in connection with assay kits that do not incorporate fiber optics, to utilize energy transfer techniques in order to achieve fluorometric determinations. An example of such an approach is found in Shaffar U.S. Pat. No. 4,495,293. Such an approach provides an assay solution that includes a fluorescer and a reagent system which is capable of providing a change in the transmittive properties of the assay solution. An objective here is the development of fluorescence energy transfer, which is the transfer of the excited state energy from the donor to an acceptor. Assay solutions utilizing this general technique are limited in their ability to be tailored in order to respond to analytes of various specific values.
By proceeding in accordance with the present invention, it has been found that the phenomenon of fluorescence energy transfer can serve as a new class of indicators for chemical sensors. These can be described as molecules whose fluorescent output follows a characteristic response allowing, for example in the case of an optrode, for single point calibration. This approach for these types of chemical sensors also provides the ability to tailor the molecule to respond, for example, at any pH by simply selecting an appropriate indicator at the desired pH value.
In summary, the present invention relates to chemical sensor components that incorporate a spacer of a known or a determinable length which tethers or binds a fluorescent, environmentally insensitive molecule to a colorimetric or other fluorometric indicator. This spacer group is substantially rigid. The extent to which the fluorescent moiety emits is dependent upon the status of the colorimetric indicator, which is in turn dependent upon the species for which it is sensitive. The absorbance spectrum of the colorimetric indicator or acceptor overlaps with the emission spectrum of the fluorescent energy donor.
It is a general object of the present invention to provide an improved indicator for a chemical sensor, such as a fiber optic chemical sensor.
Another object of this invention is to provide an improved chemical sensor that utilizes fluorescence energy transfer between a tethered pair of moieties.
Another object of the present invention is to provide an improved chemical sensor that provides a fixed distance for fluorescence energy transfer from a fluorescent donor to a colorimetric indicator.
Another object of the present invention is to provide an improved chemical sensor suitable for devices incorporating fiber optics, which sensor incorporates fluorescence energy transfer between a tethered pair of moieties wherein the degree of energy transfer is dependent only on the extent of overlap of the emission spectrum of the fluorescent component with the absorbtion spectrum of the indicator component.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.